Fears of hacking and campaign interference have simmered throughout France's high-stakes, closely watched campaign - and boiled over Friday night as Mr Macron's team said it had been the victim of a "massive and coordinated" hack.

His political movement said the unidentified hackers accessed staffers' personal and professional emails and leaked campaign finance material and contracts - as well as fake decoy documents - online.

The perpetrators remain unknown. While the hack is shaking up the campaign, it's unclear whether the document dump would dent Mr Macron's large poll lead over far-right Marine Le Pen going into the vote.

After ditching France's traditional left-right parties in a first-round election, voters are now choosing between Mr Macron's business-friendly, pro-European vision and Ms Le Pen's protectionist, closed-borders view that resonates with workers left behind by globalization.

The future of the European Union may hinge on the vote, and also seen as a test for global populism, and voting begins in France's overseas territories Saturday before moving to the mainland Sunday.

The leak began just before the nationwide blackout on campaigning and media coverage blackout descended.

Slamming the hack as an effort to "seed doubt and disinformation" and destabilise the vote, Mr Macron's movement En Marche said it would "take all measures" to shed light on what happened.

It recalled similar leaks from Hillary Clinton's US presidential campaign, which also said that authentic documents were mixed with false ones.

The commission overseeing the French campaign said in a statement that it is holding a meeting early Saturday after being informed of the hack and leak.

The voting watchdog also called on the Interior Ministry late Friday to look into claims by the Le Pen campaign that ballot papers are being tampered with nationwide to benefit Mr Macron. The Le Pen campaign said electoral administrators in several regions who receive ballot papers for both candidates have found the Le Pen ballot "systematically torn up."

The presidential campaign has been unusually bitter, with voters hurling eggs and flour, protesters clashing with police and candidates insulting each other on national television - a reflection of the widespread public disaffection with politics.

Ms Le Pen, 48, has brought her far-right National Front party, once a pariah for its racism and anti-Semitism, closer than ever to the French presidency, seizing on working-class voters' growing frustration with globalization and immigration.